Retailers like Nordstrom use surveillance to track where customers spend time in their stores

CNN - More and more retailers are using smartphones to track customers' spending habits.

The upscale department store chain Nordstrom tried it recently, and some shoppers called it an invasion of privacy when they learned about it.

Retailers use video surveillance and track signals from smart phones to monitor behavior when customers are in the stores. The in-store analytics make it possible for retailers to understand where shoppers go, where they stop and how all of their activity translates to a sale at the cash register.

Nordstrom recently ended a test program gathering pings from wifi signals on customer's smart phones as they browsed through the store. Some were outraged after learning about the in-store surveillance.

"Way over the line," one consumer wrote on facebook.

As people enter, the software pinpointed shoppers and followed them throughout the store.

Retailnext, one of the companies providing this kind of technology, said the software is so specific, it can tell exactly where inside the store a person is standing and even which direction their head is looking.

Although the technology can monitor a person's location and what that person is doing, it cannot marry it back to the shoppers' personal identity.

However, shoppers reported having mixed feelings about being watched by big brother.